Raman amplifier system and method with integrated optical time domain reflectometer

ABSTRACT

Raman amplifier systems and methods with an integrated Optical Time Domain Reflectometer (OTDR) for integrated testing functionality include an amplifier system, an OTDR and telemetry subsystem, and a method of operation. The OTDR and telemetry subsystem is configured to operate in an OTDR mode when coupled to a line in port and to operate in a telemetry mode when coupled to a line out port. The OTDR and telemetry subsystem enables on-demand fiber testing while also operating as a telemetry channel that is both a redundant optical service channel (OSC) and provides a mechanism to monitor Raman gain over time. The OTDR and telemetry subsystem minimizes cost and space by sharing major optical and electrical components between the integrated OTDR and other functions on the Raman amplifier.

FIELD OF THE INVENTION

Generally, the field of art of the present disclosure pertains to fiberoptic systems and methods, and more particularly, to Raman amplifiersystems and methods with an integrated Optical Time Domain Reflectometer(OTDR) for integrated testing functionality.

BACKGROUND OF THE INVENTION

Conventionally, OTDRs inject a series of optical pulses into the fiberunder test and extract, from the same end of the fiber, light that isscattered (i.e., Rayleigh backscatter) or reflected back from pointsalong the fiber. Results from OTDRs are used for estimating the fiber'slength, overall attenuation, and discontinuities along the fiber. Suchinformation about the fiber under test is particularly relevant in thecontext of Raman amplifiers where Raman pumps input high-poweredwavelengths in a co-propagated and/or counter-propagating manner in thefiber with information carrying wavelengths. That is, with high-poweredwavelengths, it is desirable to know about fiber conditions particularlydiscontinuities and the like. Conventionally, there have been severalattempts to integrate fiber testing functionality with Raman amplifiers.These conventional implementations can be characterized in twocategories, namely 1) use of dedicated optical components or testequipment to provide the OTDR function within a Raman amplifier or 2)use one of the Raman pump lasers as the OTDR source. Disadvantageously,dedicated optical components leads to increased cost, power, and/orspace requirements and use of one of the Raman pump lasers preventsin-service operation (i.e., no testing when the Raman pump lasers arein-service). Thus, relative to conventional systems and methods, thereis a need to integrate OTDR functionality with optical amplifier systemsand methods while minimizing cost, a need to operate the OTDRfunctionality while the optical amplifier systems and methods are eitherout-of-service or in-service, and the like.

BRIEF SUMMARY OF THE INVENTION

In an exemplary embodiment, an amplifier system includes at least onepump laser coupled to a line in port; and an optical time domainreflectometer (OTDR) and telemetry subsystem selectively coupled to theline in port and a line out port, wherein the line out port is for adifferent fiber than the line in port, and wherein the OTDR andtelemetry subsystem is configured to operate in an OTDR mode whencoupled to the line in port and to operate in a telemetry mode whencoupled to the line out port. In the OTDR mode, the transmitter can beconfigured to transmit optical pulses on the line in port and thereceiver is configured to detect back reflections associated with theoptical pulses from the line in port; and, in the telemetry mode, thetransmitter can be configured to transmit a telemetry wavelengthincluding data over the line out port to another node and the receiveris configured to receive the a telemetry wavelength including data overthe line in port from the another node. The OTDR and telemetry subsystemcan include a transmitter selectively coupled to the line in port andthe line out port via an optical switch; and circuitry communicativelycoupled to the transmitter and the receiver. The OTDR and telemetrysubsystem can further include a receiver coupled to the line in port.

The OTDR and telemetry subsystem can include a transmitter providing anout-of-band counter-propagating OTDR signal in the OTDR mode and aco-propagating out-of-band telemetry channel in the telemetry mode. Thetransmitter can include a wavelength selected outside a range of the atleast one pump laser and any wavelength division multiplexing (WDM)channels on the line in port and the line out port. The transmitter caninclude a tunable wavelength selected in a region where gain from the atleast one pump laser is near zero. The receiver can include a bandwidthof between 40 kHz and 12 MHz selected for pulse lengths of approximately10 ns to 100 us over the transmitter in the OTDR mode. In the OTDR mode,the circuitry can include a signal processing block; a pulse generatorcoupled to the signal processing block and to the transmitter; and atransimpedance amplifier coupled to the receiver and ananalog-to-digital converter, wherein the analog-to-digital converter iscoupled to the signal processing block. The signal processing block canbe configured to provide back reflection data versus distance to aprocessor associated with the amplifier system, and wherein thecircuitry can only interprets the back reflection data versus distanceto detect an open connector and the processor interprets the backreflection data versus distance data to provide an OTDR trace basedthereon. The OTDR mode can be configured to operate both while the atleast one pump laser is off and while the at least one pump laser is on,and wherein a difference between OTDR traces when the at least one pumplaser is off and when the at least one pump laser is on can beindicative of Raman gain. In the telemetry mode, the circuitry can beconfigured to provide a real-time measurement of Raman gain separatefrom any wavelength division multiplexing (WDM) channels; and provide aredundant safety shutdown mechanism.

In another exemplary embodiment, an optical module including an opticaltime domain reflectometer (OTDR) and telemetry subsystem includes atransmitter selectively coupled to a line in port of the optical moduleand a line out port of the optical module via an optical switch; areceiver coupled to the line in port; and circuitry communicativelycoupled to the transmitter and the receiver; wherein the transmitter,the receiver, and the circuitry are configured to operate in an OTDRmode when coupled to the line in port and to operate in a telemetry modewhen coupled to the line out port. The transmitter can provide anout-of-band counter-propagating OTDR signal in the OTDR mode and aco-propagating out-of-band telemetry channel in the telemetry mode. Inthe OTDR mode, the transmitter can be configured to transmit opticalpulses on the line in port and the receiver is configured to detect backreflections associated with the optical pulses from the line in port;and, in the telemetry mode, the transmitter can be configured totransmit a telemetry wavelength including data over the line out port toanother node and the receiver is configured to receive the a telemetrywavelength including data over the line in port from the another node.

The transmitter can include a wavelength selected outside a range of theat least one pump laser and any wavelength division multiplexing (WDM)channels on the line in port and the line out port. In the OTDR mode,the circuitry can include a signal processing block; a pulse generatorcoupled to the signal processing block and to the transmitter; and atransimpedance amplifier coupled to the receiver and ananalog-to-digital converter, wherein the analog-to-digital converter iscoupled to the signal processing block; wherein the signal processingblock is configured to provide back reflection data versus distance to aprocessor associated with the amplifier system, and wherein thecircuitry only interprets the back reflection data versus distance todetect an open connector and the processor interprets the backreflection data versus distance data to provide an OTDR trace basedthereon. The OTDR mode can be configured to operate both while the atleast one pump laser is off and while the at least one pump laser is on,and wherein a difference between OTDR traces when the at least one pumplaser is off and when the at least one pump laser is on is indicative ofRaman gain. In the telemetry mode, the circuitry can be configured toprovide a real-time measurement of Raman gain separate from anywavelength division multiplexing (WDM) channels; and provide a redundantsafety shutdown mechanism.

In yet another exemplary embodiment, a method includes installing andprovisioning a Raman amplifier to associated fiber plant; performing afiber plant test using an optical time domain reflectometer (OTDR) andtelemetry subsystem disposed within the Raman amplifier, wherein theOTDR and telemetry subsystem is configured to operate in an OTDR modewhen coupled to a first fiber and to operate in a telemetry mode whencoupled to a second fiber; performing corrective actions on the firstfiber responsive to the fiber plant test; turning up the Ramanamplifier; and continuously monitoring Raman gain using the OTDR andtelemetry subsystem.

BRIEF DESCRIPTION OF THE DRAWING(S)

Exemplary and non-limiting embodiments of the present disclosure areillustrated and described herein with reference to various drawings, inwhich like reference numbers denote like method steps and/or systemcomponents, respectively, and in which:

FIG. 1 is a block diagram of a Raman amplifier with an integratedOTDR/telemetry subsystem;

FIG. 2 is a graph of an exemplary OTDR trace using the Raman amplifierof FIG. 1 and the OTDR/telemetry subsystem;

FIG. 3 is a flowchart of an operational method provisioning, testing,turning up, and operating the Raman amplifier of FIG. 1;

FIG. 4 is a functional block diagram of the OTDR/telemetry subsystem inthe OTDR mode for the Raman amplifier of FIG. 1; and

FIG. 5 is a block diagram of an exemplary implementation in a system ofthe Raman amplifier of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

In various exemplary embodiments, the present disclosure relates toRaman amplifier systems and methods with an integrated Optical TimeDomain Reflectometer (OTDR) for integrated testing functionality. Inoperation, a Raman amplifier sends a very high amount of optical power(˜0.5-1 W) into fiber plant to provide gain for the data-carryingoptical channels. The OTDR allows the Raman amplifier to verify theintegrity of the fiber plant, measuring critical parameters likeinsertion loss, propagation loss, and back reflections from opticalconnectors. This provides the capability to identify potential problemsbefore the high-power Raman pumps are enabled and then to monitor thehealth of the fiber plant over time. Specifically, the Raman amplifiersystems and methods minimize cost by sharing major optical andelectrical components between the integrated OTDR and other functions onthe Raman amplifier. Further, the Raman amplifier systems and methodsprovide a mechanism to operate the OTDR both out-of-service (duringsystem provisioning) and in-service (while the system is carrying livetraffic). Also, the Raman systems and methods can use the OTDRinformation to estimate Raman gain and to track changes in the fiberplant over time.

Referring to FIG. 1, in an exemplary embodiment, a block diagramillustrates a Raman amplifier 10 with an integrated OTDR/telemetrysubsystem 12. Functionally, the Raman amplifier 10 includes threesubsystems, namely the OTDR/telemetry subsystem 12, Raman pumps 14, andan Optical Service Channel (OSC) 16. The Raman amplifier 10 is atwo-fiber device meaning the Raman amplifier 10 supports two fibers,line A and line B, with a line A in port 20, a line A out port 22, aline B in port 24, and a line B out port 26. In the exemplaryconfiguration of FIG. 1, the Raman amplifier 10 is counter-pumping lineA and monitoring line B. That is, the ports 20, 26 are facing outsidefiber plant, and the ports 22, 24 are facing internally in a node (i.e.,to other components such as EDFA amplifiers, add/drop multiplexers,wavelength selective switches, transceivers, etc.). The Raman pumps 14include one or more high-powered lasers at various Raman wavelengths(e.g., 1420-1465 nm, 1424/1434 nm, 1455/1465 nm, etc.). These lasers areadded to the line A via a 14XX wavelength division multiplexing (WDM)filter 30 that is configured to add wavelengths in the 14XX range to theline A which can include information-carrying wavelengths in the 15XXrange.

The Raman pumps 14 can include Raman pump lasers, optical depolarizationand multiplexing, control circuitry, and sensors to enable Ramanpumping. In an exemplary embodiment, a baseline pump design can includea plurality of 14XX nm pump wavelengths with total optical powers ofabout 1.0 W. The OSC 16 includes a receiver (RX) 32 that is coupled offthe line A via a 1511 nm WDM filter 34 and a transmitter (TX) 36 that isadded to the line B via a 1511 nm WDM filter 38. In this exemplaryembodiment, the OSC 16 is at 1511 nm although other wavelengths are alsocontemplated. The OSC provides a communication channel between nodes foroperations, administration, maintenance, and provisioning (OAM&P)functionality.

In the Raman amplifier 10, the OTDR/telemetry subsystem 12 has dualfunctionality of being an OTDR and a telemetry channel. TheOTDR/telemetry subsystem 12 includes a receiver (RX) 46, a transmitter(TX) 48, and circuitry 50. The receiver 46, transmitter 48, andcircuitry 50 are shared between OTDR and telemetry functions. An opticalswitch 52 is used to select one of the two modes of operation, OTDR andtelemetry. In an OTDR mode, the optical switch 52 is set to a firstposition coupling the transmitter 48 to an optical circulator 54. Theoptical circulator 54 connects to a 1527 nm WDM filter 56 (e.g., thetransmitter 48 can be at 1527 nm although other wavelengths are alsocontemplated). In an exemplary embodiment, the optical circulator 54 canbe replaced with a coupler. For example, a coupler could have additionalinsertion loss (e.g., 6 dB instead of 2 dB for the optical circulator54) which would reduce the dynamic range of the OTDR, but would be costreduced. The WDM filter 56 couples the transmitter 48 to the line A.Also, the WDM filter 56 couples the line A to the receiver 46 for backreflection detection. In the OTDR mode, the circuitry 50 is configuredto transmit an OTDR pulse via the transmitter 48 that is launchedbackward in the line A into the port 20, i.e. the OTDR pulse iscounter-propagating relative to any WDM channels on line A. The Ramanpumps 14, when active, are launched in the same direction as the OTDRpulse. The OTDR pulse produces a back-scattered signal, which reflectsback into the port 20 entering the Raman amplifier 10 in the forwarddirection. The optical circulator 54 then directs the back-scatteredsignal into the receiver 46, where it is digitized and analyzed by thecircuitry 50 or other devices such as a shelf processor.

In telemetry mode, the optical switch 52 is set to a second positioncoupling the transmitter 48 to the port 26, where a telemetry signalfrom the transmitter 48 co-propagates with WDM channels in that line Bfiber. With the optical switch 52 in the second position, thetransmitter 48 is inserted into the line B via a 1527 nm WDM filter 58.In this mode, the transmitter 26 allows the Raman amplifier 10 tocommunicate or signal to another Raman amplifier 10 provisioned at anupstream node in a fiber optic system. That upstream Raman amplifier 10can communicate back to the Raman amplifier 10 by sending a signal at asimilar wavelength into the line A port 20, where it is split off viathe WDM filter 56 and the optical circulator 54 to the receiver 46. Thuswith the use of the optical switch 52 and the optical circulator 54, thereceiver 46 and the transmitter 48 can be shared between the OTDR andtelemetry applications.

Thus, OTDR/telemetry subsystem 12 can be an out-of-bandcounter-propagating OTDR or a co-propagating out-of-band telemetrychannel used to actively measure the Raman gain. Both of these signalsare near 1527 nm, i.e. both these signals are the same wavelength basedon sharing the transmitter 48. The OTDR functionality can be used duringtest and turn up to ensure the fiber span and connectors meet necessaryrequirements for activating the Raman pumps 14. The telemetryfunctionality is used to actively measure the Raman gain during normaloperation. During normal operation, the OTDR functionality can beremotely enabled via software to switch the optical switch 52 to alsoenable on-demand OTDR testing in-service. Note, the circuitry 50 isconfigured to function as an OTDR, i.e. transmitting pulses andmeasuring back-scatter, and as a telemetry channel, i.e. transmittedmodulated data and receiving the same. The circuitry 50 is alsocommunicatively coupled to a node controller, shelf processor, etc. forconveying data from the OTDR/telemetry subsystem 12. For example, in theOTDR mode, the circuitry 50 can deliver calibrated back reflection dataversus distance to the shelf processor via standard intra-shelfcommunications protocols. Also, the OTDR/telemetry subsystem 12 can becommanded into the OTDR mode of the telemetry mode by the shelfprocessor.

The OTDR/telemetry subsystem 12 can perform several functions in thetelemetry mode. First, the transmitter 48 provides a real timemeasurement of the Raman gain separate from any WDM channels. This maybe used for long term monitoring of the health of the fiber plant andRaman amplifier 10, and may also be used for relatively rapid real timecontrol. The telemetry channel also works in parallel with the OSC 16and other sensors to provide robust and redundant fault monitoring. Thatis, the telemetry mode of the OTDR/telemetry subsystem 12 provides asecond OSC channel for redundancy. In some cases Raman amplificationmust be used on very high loss span that exceed the OSC link budget(e.g., festoon or channel crossings), and in these cases an opticalsensor redundant to the OSC channel is needed to provide for acceptablefault management and eye safety protocols. The telemetry channelprovides a redundant safety mechanism, meaning that the Raman amplifier10 is able to distinguish between a fiber cut (affects theOTDR/telemetry subsystem 12 and the OSC 16) and an OSC failure (affectsthe OSC 16 only). The telemetry channel can also be used to communicatebetween nodes, but at a much lower data rate compared to the OSC 16.

In an exemplary embodiment of the Raman amplifier 10, the wavelengththat has been selected for the transmitter 48 in the OTDR/telemetrysubsystem 12 is 1527 nm. This enables this signal to coexist with theRaman pumps (e.g., 1420-1470 nm) and WDM channels (e.g., 1527.5-1567 nm)without interference. Any wavelength between the Raman pump wavelengthsand the WDM channel wavelengths can be used. In particular, this makesit possible for the OTDR to be used in-service, i.e. while the WDMchannels are active. In the absence of the Raman pump, the OTDR providesa measure of the propagation and interconnection losses in the fiberplant. Referring to FIG. 2, in an exemplary embodiment, a graphillustrates an exemplary OTDR trace 60 using the Raman amplifier 10 andthe OTDR/telemetry subsystem 12. The OTDR trace 60 includes two traces62, 64, an OTDR trace 62 with Raman pumps off and an OTDR trace 64 withRaman pumps on. With the Raman pumps enabled, the 1527 nm OTDR pulseexperiences gain as it propagates down the fiber, which affects the OTDRtrace as shown in the OTDR trace 64. By comparing these two traces 62,64, it is possible to estimate the Raman gain in the fiber after thepumps are turned on. Then by measuring the OTDR trace periodically, onecan monitor the health of the system as changes in fiber loss or Ramangain create a corresponding change in the OTDR traces 62, 64. This canprovide a powerful new diagnostic tool for network operators.

In another exemplary embodiment, the transmitter 48 can be tunableallowing for different OTDR wavelengths (and telemetry wavelengths).Alternatively, the transmitter 48 can include separate transmitterscontained therein at different wavelengths. This can be used to monitorRaman gain and fiber loss separately. By switching the OTDR wavelengthto a region where the Raman gain is near zero (e.g., 1610 nm), fiberlosses could be measured accurately in-service via an OTDR measurement,independently of the Raman gain. With a tunable wavelengthimplementation of the transmitter 48, there could be a potential tomeasure the Raman gain within the WDM signal band as well in-service, bytuning the OTDR wavelength to any unused WDM channels. Also, thisexemplary embodiment requires the WDM filter 56 be tunable as well totrack the wavelength tuning of the transmitter 48.

As described herein, the OTDR/telemetry subsystem 12 is embedded intothe Raman amplifier 10. Note, the Raman amplifier 10 can be realized asa module, circuit pack, line card, “pizza box”, subsystem, and the likefor operation in a larger, WDM system. Also, the OTDR/telemetrysubsystem 12 contemplates operation in other modules besides the Ramanamplifier 10, such as an erbium doped fiber amplifier (EDFA) module, anOSC module, etc. The OTDR function of the OTDR/telemetry subsystem 12generates calibrated back reflection versus distance data files that canbe used by a shelf processor. In an exemplary embodiment, the OTDRfunction in the amplifier pack does not interpret the traces, except ifthe connector back-reflection is so large that it represents an openconnector, in which case the Raman amplifier 10 will not turn on. Theshelf processor, which can include general purpose and/or specialpurpose processing logic, can be used to perform the data analysis ofthe data files thereby removing processing complexity from theOTDR/telemetry subsystem 12.

Advantageously, the OTDR function ensures that connectors havesufficiently low loss and low back reflection so that the Ramanamplifier 10 operates properly and connectors will not be damaged at ˜1W Raman pump levels. Experimental work indicates that back reflection ofless than −45 dB results in a robust and resilient connectors that willnot be damaged by optical power, and minimizes and multi-pathinterference (MPI) effects that could degrade system performance. In anexemplary embodiment, the OTDR is able to accurately measure a −45 dBback-reflection within 0-1000 meters of the Raman amplifier 10 with asignal-to-noise ratio, SNR>10 dB. The OTDR function is also able toresolve back reflections from local connectors. For example, localconnectors generally include connectors in a same location as the Ramanamplifier 10 such as on a front panel on the Raman amplifier 10, atfiber distribution frames, etc. These connectors can be spaced as closedas 2-3 meters apart from each other in practice.

Referring to FIG. 3, in an exemplary embodiment, a flowchart illustratesan operational method 70 provisioning, testing, turning up, andoperating the Raman amplifier 10. Advantageously, the Raman amplifier 10provides an integrated system enabling automated provisioning, test, andturn up capabilities to minimize complexities faced by a serviceprovider as well as in-service monitoring over time. The operationalmethod 70 provides an exemplary use of the Raman amplifier 10 in anoptical network. First, the Raman amplifier 10 is installed (step 71).That is, the Raman amplifier 10 is physically placed in a system, shelf,frame, etc. and provided power, etc. The Raman amplifier 10 isprovisioned and coupled to fiber plant (step 72). Prior to activatingthe Raman pumps 14, the fiber plant is test via the OTDR function of theRaman amplifier 10 and any corrective action is taken based thereon(step 73). For example, many real-world problems with Raman amplifiersoccur due to non-ideal conditions associated with the inside and outsideplant fiber such as connector losses, excess bend losses in conduits,unanticipated outside plant fiber loss or point losses, and improperlycharacterized fiber type. Subsequent to the test, corrective action canbe taken to improve any problems. The integrated OTDR can be used toeliminate nearly all of the uncertainty that may exist when deployingRaman amplifiers, permitting nearly autonomous provisioning, test andturn up capabilities.

Once corrective actions are taken (if any), the Raman amplifier 10 canbe turned up enabling the Raman pumps 14 (step 74). Here, the Ramanamplifier 10 can switch from the OTDR functionality of theOTDR/telemetry subsystem 12 to the telemetry functionality. The Ramanamplifier 10 can continuously measure real-time Raman gain whileconcurrently providing a redundant OSC channel via the telemetryfunctionality (step 75). During the continuous measurement, if there areRaman gain issues or periodically (step 76), the Raman amplifier 10 canswitch from the telemetry functionality to the OTDR functionality andperform in-service fiber plant testing and take any corrective actionbased thereon (step 77).

Referring to FIG. 4, in an exemplary embodiment, a functional blockdiagram illustrates the OTDR/telemetry subsystem 12 in the OTDR mode.FIG. 4 illustrates only components in the Raman amplifier 10participating the OTDR mode. Specifically, the optical circulator 54 hasa port coupled to a fiber connector 82 that ultimately connects to fiberunder test (FUT) 84. Note, the optical circulator 54 can also be adirectional coupler or any other three-port device that enables both thetransmitter 48 and the receiver 46 to connect to the FUT 84. FIG. 4 alsoincludes additional details in the circuitry 50 related to the OTDRmode. On the transmitter 48 side, the circuitry 50 includes a pulsegenerator 86 connected to a signal processing block 88. Collectively,the pulse generator 86 and the signal processing block 88 are configuredto generate specific length pulses to drive/modulate the transmitter 48.Note, the pulse length for the transmitter 48 correlates to how muchbandwidth is required in the receiver 46. Without reflections in the FUT84, different pulse widths will achieve similar OTDR slope or fiber lossprofile, but one purpose of the ODTR is to measure possible backreflection and location. This requires a short pulse.

It has been determined that a pulse width of between 10 ns and 100 us isacceptable. Preferably, shorter pulses (e.g., about 10 ns for thetransmitter 48) are used for measuring the first few km's of the FUT 84.For longer distances (e.g., 100 km), much longer pulses can be used suchas 10 us and the like. In this case, the bandwidth of the receiver canbe reduced considerably to less than 100 kHz. For example, the Ramanamplifier 10 is most concerned about back reflection close to the port20 as this is where there are safety and equipment concerns withhigh-powered lasers. That is, the OTDR mode of the OTDR/telemetrysubsystem 12 is primarily concerned with detecting fiber related issuesimpairing Raman operation. In an exemplary embodiment, the OTDR mode isconfigured to measure about 4% back reflection within about the first 30km of the FUT 84 using a 10 ns pulse. For a 10 ns pulse, ideally 100 MHzbandwidth is required on the receiver 46 although this can be reducedfor cost reduction without significant impact in performance to about 15MHz. In an exemplary embodiment, the receiver 46 bandwidth can vary from40 kHz to 12 MHz and the pulse length can vary from 10 ns to 100 us.

On the receive side, the receiver 46 connects to an amplifier 90 whichconnects to an analog-to-digital (A/D) device 92 that connects to thesignal processing block 88. Note, the circuitry 50 includes both digitaland analog components. The signal processing block 88 can beall-digital. The amplifier 90 can be integrated with the receiver 46 orin the circuitry 50, and the amplifier 90 is configured to amplifycurrent from the receiver 46 and to provide the amplified current to theA/D device 92 for digitization. The amplifier 90 can include atransimpedance amplifier (TIA). As described above, the receiver 46 canhave a bandwidth of between 15-100 MHz (preferably 15 MHz) with adynamic range of at least 58-73 dB (0 km-30 km with 10 ns pulse). In anexemplary embodiment, the receiver 46 can be an avalanche photodiode(APD) receiver.

In addition to detecting back reflection within about the first 30 km,the OTDR function can be able to determine transmission fiber loss over˜100 km so that loss profiles can be compared to stored or previouslyobtained values. This can require a different operating mode (differentpulse width, repetition rate, etc) that the mode used to measure andresolve connector back reflections. In this exemplary embodiment, thepulse generator 86 and the signal processing block 88 are configurableto adjust the operating mode. The OTDR function can also be availableafter a fiber cut and repair to repeat the provisioning, test and turnup process. Manual operation can be available during the fiber cut eventso that service provider personnel can use the OTDR to locate the fibercut. Also, as described herein, the OTDR wavelength should be out of thesignal band, to permit low loss multiplexing into the transmissionfiber.

Referring to FIG. 5, in an exemplary embodiment, a block diagramillustrates an exemplary implementation in a system 100 of the Ramanamplifier 10. The system 100 can include a point-of-presence (POP) or aline amplifier (LA) site with the Raman amplifier 10 operating in a WDMnetwork element. The POP/LA site can include various fiber-relatedcomponents such as a fiber distribution frame (FDF) 102 and otherequipment such as communication support equipment (CSE) 104. The POP/LAsite has fiber that goes out to outside plant (OSP) 106. As those ofordinary skill in the art will recognize, there can be numerousconnectors in the POP/LA site that are extremely close to the Ramanamplifier 10 and its high-powered Raman pumps 14. For example, the ports20, 26 can have connectors and the FDF 102 can have various connectors110 as well. The connectors can be SC (standard connectors), LC (littleconnectors), FC (fiber connectors), etc. Importantly, the OTDR functionneeds to resolve connector problems insider the POP/LA site to ensuregood connectors (i.e., less than −45 dB back reflection) in order forthe Raman amplifier 10 to turn on. Minimum distances can be as small as2 m between the Raman amplifier 10 and the FDF 102. This resolutioninside the POP/LA site sets the lower bound on the OTDR pulse width anddetection requirements, i.e. need to be able to measure pulse height of−45 dB back reflection.

It will be appreciated that some exemplary embodiments described hereinmay include one or more generic or specialized processors (“one or moreprocessors”) such as microprocessors, digital signal processors,customized processors, and field programmable gate arrays (FPGAs) andunique stored program instructions (including both software andfirmware) that control the one or more processors to implement, inconjunction with certain non-processor circuits, some, most, or all ofthe functions of the methods and/or systems described herein.Alternatively, some or all functions may be implemented by a statemachine that has no stored program instructions, or in one or moreapplication specific integrated circuits (ASICs), in which each functionor some combinations of certain of the functions are implemented ascustom logic. Of course, a combination of the aforementioned approachesmay be used. Moreover, some exemplary embodiments may be implemented asa non-transitory computer-readable storage medium having computerreadable code stored thereon for programming a computer, server,appliance, device, etc. each of which may include a processor to performmethods as described and claimed herein. Examples of suchcomputer-readable storage mediums include, but are not limited to, ahard disk, an optical storage device, a magnetic storage device, a ROM(Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM(Erasable Programmable Read Only Memory), an EEPROM (ElectricallyErasable Programmable Read Only Memory), Flash memory, and the like.When stored in the non-transitory computer readable medium, software caninclude instructions executable by a processor that, in response to suchexecution, cause a processor or any other circuitry to perform a set ofoperations, steps, methods, processes, algorithms, etc.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure andare intended to be covered by the following claims.

What is claimed is:
 1. An amplifier system, comprising: at least oneRaman pump laser optically coupled to a line in port; and an opticaltime domain reflectometer (OTDR) and telemetry subsystem selectivelyoptically coupled to the line in port and a line out port, wherein theline out port connects to a second line in port, each of the line outport and the second line in port are connected to a first fiber, and theline in port connects to a second line out port, wherein each of theline in port and the second line out port are connected to a secondfiber, and wherein the OTDR and telemetry subsystem is configured tooperate in an OTDR mode for the second fiber when coupled to the line inport and to operate in a telemetry mode for the first fiber when coupledto the line out port to measure gain due to the at least one Raman pumplaser.
 2. The amplifier system of claim 1, wherein, in the OTDR mode, atransmitter is configured to transmit optical pulses on the line in portand a receiver is configured to detect back reflections associated withthe optical pulses from the line in port; and wherein, in the telemetrymode, the transmitter is configured to transmit a telemetry wavelengthcomprising data over the line out port to another node and the receiveris configured to receive the telemetry wavelength comprising data overthe line in port from the another node.
 3. The amplifier system of claim1, wherein the OTDR and telemetry subsystem comprises: a transmitterselectively coupled to the line in port and the line out port via anoptical switch; and circuitry communicatively coupled to the transmitterand a receiver.
 4. The amplifier system of claim 1, wherein the OTDR andtelemetry subsystem comprises: a receiver coupled to the line in port.5. The amplifier system of claim 1, wherein the OTDR and telemetrysubsystem comprises a transmitter providing an out-of-bandcounter-propagating OTDR signal in the OTDR mode and a co-propagatingout-of-band telemetry channel in the telemetry mode.
 6. The amplifiersystem of claim 2, wherein the transmitter utilizes a wavelengthselected outside a range of the at least one pump laser and anywavelength division multiplexing (WDM) channels on the line in port andthe line out port.
 7. The amplifier system of claim 6, wherein thetransmitter utilizes a tunable wavelength selected in a region wheregain from the at least one pump laser is near zero.
 8. The amplifiersystem of claim 2, wherein the receiver comprises a bandwidth of between40 kHz and 12 MHz selected for pulse lengths of approximately 10 ns to100 μs over the transmitter in the OTDR mode.
 9. The amplifier system ofclaim 2, wherein, in the OTDR mode, the circuitry comprises: a signalprocessing block; a pulse generator coupled to the signal processingblock and to the transmitter; and a transimpedance amplifier coupled tothe receiver and an analog-to-digital converter, wherein theanalog-to-digital converter is coupled to the signal processing block.10. The amplifier system of claim 9, wherein the signal processing blockis configured to provide back reflection data versus distance to aprocessor associated with the amplifier system, and wherein thecircuitry only interprets the back reflection data versus distance todetect an open connector and the processor interprets the backreflection data versus distance data to provide an OTDR trace basedthereon.
 11. The amplifier system of claim 2, wherein the OTDR mode isconfigured to operate both while the at least one pump laser is off andwhile the at least one pump laser is on, and wherein a differencebetween OTDR traces when the at least one pump laser is off and when theat least one pump laser is on is indicative of Raman gain.
 12. Theamplifier system of claim 2, wherein, in the telemetry mode, thecircuitry is configured to: provide a real-time measurement of Ramangain separate from any wavelength division multiplexing (WDM) channels;and provide a redundant safety shutdown mechanism.
 13. An optical modulecomprising an optical time domain reflectometer (OTDR) and telemetrysubsystem, comprising: a transmitter selectively coupled to a line inport of the optical module and a line out port of the optical module viaan optical switch, wherein the line out port connects to a second linein port, each of the line out port and the second line in port areconnected to a first fiber, and the line in port connects to a secondline out port, wherein each of the line in port and the second line outport are connected to a second fiber; a receiver coupled to the line inport; and circuitry communicatively coupled to the transmitter and thereceiver; wherein the transmitter, the receiver, and the circuitry areconfigured to operate in an OTDR mode for the second fiber whenoptically coupled to the line in port and to operate in a telemetry modefor the first fiber when optically coupled to the line out port tomeasure gain due to at least one Raman pump laser optically coupled tothe line in port.
 14. The optical module of claim 13, wherein thetransmitter provides an out-of-band counter-propagating OTDR signal inthe OTDR mode and a co-propagating out-of-band telemetry channel in thetelemetry mode.
 15. The optical module of claim 13, wherein, in the OTDRmode, the transmitter is configured to transmit optical pulses on theline in port and the receiver is configured to detect back reflectionsassociated with the optical pulses from the line in port; and wherein,in the telemetry mode, the transmitter is configured to transmit atelemetry wavelength comprising data over the line out port to anothernode and the receiver is configured to receive the a telemetrywavelength comprising data over the line in port from the another node.16. The optical module of claim 13, wherein the transmitter utilizes awavelength selected outside a range of the at least one pump laser andany wavelength division multiplexing (WDM) channels on the line in portand the line out port.
 17. The optical module of claim 13, wherein, inthe OTDR mode, the circuitry comprises: a signal processing block; apulse generator coupled to the signal processing block and to thetransmitter; and a transimpedance amplifier coupled to the receiver andan analog-to-digital converter, wherein the analog-to-digital converteris coupled to the signal processing block; wherein the signal processingblock is configured to provide back reflection data versus distance to aprocessor associated with the amplifier system, and wherein thecircuitry only interprets the back reflection data versus distance todetect an open connector and the processor interprets the backreflection data versus distance data to provide an OTDR trace basedthereon.
 18. The optical module of claim 13, wherein the OTDR mode isconfigured to operate both while the at least one pump laser is off andwhile the at least one pump laser is on, and wherein a differencebetween OTDR traces when the at least one pump laser is off and when theat least one pump laser is on is indicative of Raman gain.
 19. Theoptical module of claim 13, wherein, in the telemetry mode, thecircuitry is configured to: provide a real-time measurement of Ramangain separate from any wavelength division multiplexing (WDM) channels;and provide a redundant safety shutdown mechanism.
 20. A method,comprising: installing and provisioning a Raman amplifier comprising afirst set of ports and a second set of ports configured to connect toassociated fiber plant, wherein the first set each connect to a firstfiber and the second set each connect to a second fiber; performing afiber plant test using an optical time domain reflectometer (OTDR) andtelemetry subsystem disposed within the Raman amplifier, wherein theOTDR and telemetry subsystem is configured to operate in an OTDR modewhen optically coupled to the first fiber and to operate in a telemetrymode when optically coupled to the second fiber to measure gain due tothe Raman amplifier optically coupled to the associated fiber plant;performing corrective actions on the first fiber responsive to the fiberplant test; turning up the Raman amplifier; and continuously monitoringRaman gain using the OTDR and telemetry subsystem.